Tool changing assemblies for automated changing of tools, together with corresponding tool magazines, are essential parts of modern program-controlled machine tools, because they permit continuous complex machining even of complicated works by means of different tools. The changing steps themselves and the motions required to this end from the changing device and the tool magazine, respectively, are controlled by the controller of the machine tool in accordance with the set program. Due to their outstanding importance to the machining performance in the respective machine tool, a variety of different types and designs of tool changing assemblies have been developed in recent years, those assemblies being adapted to a greater or lesser extent to the design and mode of operation of the associated machine tool. A requirement common to all known designs of tool changing assemblies is that the various changing operations must be performed within the shortest possible time so that the necessary idle times of the machine are minimized. As a rule, this requirement is satisfied only by correspondingly complex machines. This complexity is due to the dimensions of the drive units and the moving parts as well as the control means. The costs of such efforts may by justified in the case of large machining centers, but for smaller machine tool operations, this large cost is often not acceptable by customers and users.
An example of a related machine is shown in German Gebrauschmuster No. 86 28 623.4 which discloses a tool changing assembly for program controlled universal milling and drilling machines, the assembly serving both the vertical and the horizontal spindle. A horizontal cross-member is rigidly mounted in a sidewall of the machine stand. A bracket is supported on the cross-member for axial movement and power-driven pivoting movement within a predetermined angular range. This bracket, which is arranged parallel with the wall of the stand, has a rearwardly right-angularly bent support member mounted thereon for rotation therewith and for movement in the axial direction. The support member carries a cross-arm which is rotatable about the longitudinal axis thereof and has gripping pliers disposed perpendicularly to the longitudinal axis of the cross-arm. In this known tool changing assembly the bracket, the support member mounted on the end thereof, the cross-arm and the gripping pliers perform different movements during each changing process, those movements being respectively generated by separate drive units. The arms, which are designed for extremely fast and accurate movements, and the correspondingly dimensioned drive units together with their hydraulic and electric power supply means, necessitate considerable technical effort.